A quick learner from Beaumont, TX, United States says:
December 14, 2015
Hey
This is the upper sash balance. The bottom sash balance is a spiral sash (same as Series 500).
The diameter of the sheath (if you like) is 7/16". The length of balance is 29 1/2". Other dimensions are in the pics.
I've looked and cannot find anything like this.
Cheers
Peter
Paul from SWISCO responded:
December 17, 2015
Hey, Peter. This is an old balance that isn't being made anymore, but fortunately our S500-30 should be able to replace it. I would also recommend the Red Tip color option, an a 17-012 bracket so that it can attach to the sash.